Method and apparatus for correcting spinal deformity

ABSTRACT

An apparatus ( 10 ) for correcting spinal deformity comprises at least one anchor ( 20 ) for implantation into a vertebral body ( 90 ). The anchor ( 20 ) includes a platform ( 24 ) having a first surface ( 38 ) for facing the vertebral body ( 90 ). The platform ( 24 ) includes a tunnel ( 40 ) and at least one passage ( 44 ) extending through the platform. The passage ( 44 ) extends transverse to and intersects the tunnel ( 40 ). The anchor ( 20 ) includes screw means ( 50, 52 ) for embedding into the vertebral body ( 90 ). A removable rod ( 70 ) extends into the tunnel ( 40 ) and has at least one opening ( 72 ) for receiving a cable ( 120 ) connected with another anchor ( 20 ) in another vertebral body ( 92 ). The cable ( 120 ) is tensioned to cause relative movement between the vertebral bodies ( 90  and  92 ) and thereby correct the spinal deformity. Additional cables ( 150, 170 ) may be connected to the anchors ( 20 ) and tensioned to achieve correction in multiple planes.

RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 09/812,085, filed Mar. 19, 2001, which is itself acontinuation-in-part of co-pending U.S. patent application Ser. No.09/781,847, filed Feb. 14, 2001, which is itself a continuation-in-partof co-pending U.S. patent application Ser. Nos. 09/708,940 and09/708,292, both which were filed Nov. 8, 2000. The entire subjectmatter of the aforementioned four co-pending applications isincorporated herein by reference.

TECHNICAL FIELD

The present invention is directed to a method and apparatus forcorrecting a spinal deformity, such as scoliosis, kyphosis, and/orlordosis.

BACKGROUND OF THE INVENTION

A wide variety of instrumentation and methods for use thereof are knownfor the correction of spinal deformities, such as scoliosis, kyphosis,and lordosis. Many of the known instruments utilize bone screws, alsoreferred as bone anchors, that are implanted into vertebrae. Onceimplanted, the bone screws are used to mount suitable spinal fixationinstrumentation, such as clamps, rods, and plates. Such spinalinstrumentation is then used to achieve and maintain correction of thespinal deformity and stabilize the corrected vertebrae while thevertebrae fuse together.

Most known bone screws use a conventional screw design, i.e. a solidshank, with one or more external thread convolutions. The solid shankand external threads of the conventional bone screws can cause the bonescrews to displace an undesirably large amount of bone when implanted.Such conventional bone screws typically require a large amount of torqueto implant the screw into a vertebral body. Furthermore, the resistanceof the conventional screw to being pulled axially from the bone isdependent upon the surface area of the bone that interfaces with thescrew threads.

It is also known to use a corkscrew-style helical spike as a tissueanchor. The known corkscrew-style tissue anchors, when implanted,displace less bone than the conventional bone screws, but are generallynot able to withstand high tensile loads without structural failure.European Patent No. 0 374 088 A1 discloses a bone screw having atwin-corkscrew design. In this twin-corkscrew design, which is formed bydrilling a passage up through a screw having a solid shank and thenmachining out the material between the two corkscrews, the junction ofthe corkscrews with the shank is unlikely to be capable of structurallywithstanding high tensile loads and repetitive fatigue loads. Thisstructural weakness in the design of the screw in the EP 0 374 088document is further compounded by the corkscrews having a larger overalldiameter than the head of the screw where torque is applied.

One of the more challenging applications of a bone screw is implantationof the screw into the cancellous bone of a vertebral body.Unfortunately, many of the known bone screws, such as those describedabove, can be susceptible to toggling in the vertebral body and can alsopull out of the vertebral body due to the substantial forces on thescrews from human body movement and muscle memory. In order to achieve ahigh pull-out resistance, it is common to use additional screws, whichresults in an undesirably large amount of bone being displaced.Alternatively, in order to achieve a high pull-out resistance, it isalso known to thread a bone screw all of the way through a vertebrae andplace a nut on the opposite side. However, use of such a nut increasesthe complexity of the surgical procedure.

As mentioned above, implanted bone screws are typically used to mountspinal fixation instrumentation, which is then used to achieve andmaintain correction of a spinal deformity, such as scoliosis. Variousmethods and associated fixation instrumentation are known for achievingcorrection of a spinal deformity, but most are limited by the relativelylow pull-out resistance of the known bone screws. New methods and newspinal instrumentation for achieving correction of a spinal deformitywould be possible if screws with a higher pull-out resistance wereavailable.

Hence, it is desirable to provide an apparatus for implantation intovertebrae in a minimally invasive endoscopic procedure with a reducedamount of insertion torque required. The desirable apparatus would, whenimplanted, be highly resistant to toggling in the vertebrae and to beingpulled out of the vertebrae despite the substantial forces on theapparatus from human body movement and muscle memory. Further, thedesirable apparatus could enable, and even include, new spinalinstrumentation and methods for correcting spinal deformity.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for correcting spinaldeformity. The apparatus comprises at least one anchor for implantationinto a vertebral body. The at least one anchor includes a platformhaving a first surface for facing the vertebral body. The platformincludes a tunnel and at least one passage extending through theplatform. The at least one passage extends transverse to the tunnel andintersects the tunnel. The at least one anchor includes screw means forembedding into the vertebral body upon rotation of the platform. Thescrew means projects from the first surface on the platform and extendsalong a longitudinal axis. A removable rod extends into the tunnel inthe platform. The removable rod has at least one opening for receiving acable connected with another vertebral body.

In accordance with another feature of the present invention, anapparatus for correcting spinal deformity is provided. The apparatuscomprises first and second anchors for implantation into first andsecond vertebral bodies, respectively. Each of the first and secondanchors includes a platform having a tunnel and at least one passageextending through the platform. The at least one passage in each of theanchors extends transverse to and intersects the tunnel in each of theanchors. Each of the first and second anchors further includes screwmeans for embedding into a respective one of the vertebral bodies uponrotation of the platform. The screw means projects from the platform oneach of the first and second anchors. A first removable rod extends intothe tunnel in the platform of the first anchor and a second removablerod extends into the tunnel in the platform of the second anchor. Eachof the removable rods has at least one opening. At least one cableextends through the at least one opening in each of the removable rods.The at least one cable is tensionable to cause relative movement betweenthe first and second vertebral bodies.

In accordance with yet another feature of the present invention, anapparatus for correcting spinal deformity is provided. The apparatuscomprises at least two anchors for implantation into separate vertebralbodies, respectively. Each of the at least two anchors includes aplatform having a tunnel and at least one passage extending through theplatform. The at least one passage in each of the at least two anchorsextends transverse to and intersects the tunnel in each of the anchors.Each of the at least two anchors further includes screw means forembedding into a respective one of the vertebral bodies upon rotation ofthe platform. The screw means projects from the platform on each of theat least two anchors. A first removable rod extends into the tunnel inthe platform of one of the at least two anchors and a second removablerod extends into the tunnel in the platform of another of the at leasttwo anchors. Each of the removable rods has at least one opening. Atleast one cable extends through the at least one opening in each of theremovable rods. The at least one cable is tensionable to cause relativemovement between the vertebral bodies. A spinal fixation implant extendsbetween and connects with the platform on each of the at least twoanchors.

In accordance with still another feature of the present invention, amethod for correcting spinal deformity is provided. According to theinventive method, at least two anchors are provided for implantationinto separate vertebral bodies. Each of the at least two anchorsincludes a platform having a tunnel and at least one passage extendingthrough the platform. The at least one passage extends transverse to thetunnel and intersects the tunnel. Each of the at least two anchorsfurther includes screw means for embedding into one of the vertebralbodies upon rotation of the platform. At least two removable rods arealso provided, each of which has a plurality of transversely extendingopenings. The at least two anchors are implanted in the separatevertebral bodies. A respective one of the removable rods is insertedinto the tunnel in each of the at least two anchors. One of theplurality of openings in each of the removable rods is then aligned withthe at least one passage in each of the platforms. Connecting means isinserted into each of the aligned one of the plurality of openings andthe at least one passage to connect a respective one of the at least tworemovable rods with each of the at least two anchors. Next, the at leasttwo anchors are connected with at least one cable that extends throughanother of the plurality of openings in each of the removable rods. Theat least one cable is then tensioned to cause relative movement betweenthe vertebral bodies.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a first embodiment of the presentinvention;

FIG. 2 is a sectional view taken along line 2—2 in FIG. 1;

FIG. 3 is a sectional view taken along line 3—3 in FIG. 1;

FIG. 3A is a view similar to FIG. 3 illustrating an alternateconfiguration;

FIG. 4 is a sectional view taken along line 4—4 in FIG. 1;

FIG. 4A is a view similar to FIG. 4 illustrating an alternateconfiguration;

FIG. 5 is an exploded perspective view of the apparatus of FIG. 1, andalso illustrates a driver for rotating the apparatus;

FIG. 6 is a schematic anterior view illustrating the apparatus of FIG. 1implanted in a vertebrae;

FIG. 7 illustrates an alternate configuration for an end portion of theapparatus of FIG. 1;

FIG. 8 is a schematic side view illustrating several vertebral bodiesimplanted with the apparatus of FIG. 1 and connected by a cable inaccordance with the present invention, the vertebral bodies being shownin a first condition prior to correction;

FIG. 9 is a schematic view similar to FIG. 8 illustrating the vertebralbodies in a second condition following correction;

FIG. 10 is a schematic view similar to FIG. 9 illustrating a spinalfixation implant constructed in accordance with the present inventionand connected to the apparatus in each of the vertebral bodies;

FIG. 11 is a schematic anterior view taken along line 11—11 in FIG. 10;

FIG. 12 is a schematic anterior view of several thoracic vertebrae in aspine having scoliosis and kyphosis, each of the vertebrae beingimplanted with the apparatus of FIG. 1 and connected by a cable inaccordance with the present invention;

FIG. 13 is a schematic view similar to FIG. 12 illustrating thepositions of the vertebrae following correction of the scoliosis;

FIG. 14 is a schematic side view taken along line 14—14 in FIG. 13showing the kyphosis;

FIG. 15 is a schematic side view similar to FIG. 14 showing anothercable extending between the vertebrae prior to correction of thekyphosis;

FIG. 16 is a schematic view similar to FIG. 15 illustrating thepositions of the vertebrae following correction of the kyphosis;

FIG. 17 is a schematic side view similar to FIG. 16 illustrating aspinal fixation implant constructed in accordance with the presentinvention and connected to the apparatus in each of the vertebralbodies;

FIG. 18 is a schematic anterior view of several lumbar vertebrae in aspine having scoliosis and lordosis, each of the vertebrae beingimplanted with the apparatus of FIG. 1 and connected by a cable inaccordance with the present invention;

FIG. 19 is a schematic view similar to FIG. 18 illustrating thepositions of the vertebrae following correction of the scoliosis;

FIG. 20 is a schematic side view taken along line 20—20 in FIG. 19showing the lordosis;

FIG. 21 is a schematic side view of the vertebrae shown in FIG. 20 andillustrating yet another cable extending between the vertebrae prior tocorrection of the lordosis;

FIG. 22 is a schematic view similar to FIG. 21 illustrating thepositions of the vertebrae following correction of the lordosis;

FIG. 23 is a schematic side view similar to FIG. 22 illustrating aspinal fixation implant constructed in accordance with the presentinvention and connected to the apparatus in each of the vertebralbodies;

FIG. 24 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a second embodiment of the presentinvention;

FIG. 25 is a sectional view taken along line 25—25 in FIG. 24;

FIG. 26 is a sectional view taken along line 26—26 in FIG. 25;

FIG. 27 is a sectional view taken along line 27—27 in FIG. 24;

FIG. 28 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a third embodiment of the presentinvention;

FIG. 29 is a sectional view taken along line 29—29 in FIG. 28;

FIG. 30 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a fourth embodiment of the presentinvention;

FIG. 31 is a sectional view taken along line 31—31 in FIG. 30;

FIG. 32 is a sectional view taken along line 32—32 in FIG. 30;

FIG. 32A is a schematic view similar to FIG. 32 illustrating analternate configuration;

FIG. 33 is a sectional view taken along line 33—33 in FIG. 30;

FIG. 33A is a schematic view similar to FIG. 33 illustrating analternate configuration;

FIG. 34 is a schematic side view, partially in section, illustrating theapparatus of FIG. 30 in a first condition prior to implantation in avertebrae;

FIG. 35 is a schematic view similar to FIG. 34 illustrating theapparatus of FIG. 30 during implantation in the vertebrae;

FIG. 36 is a schematic view similar to FIG. 34 illustrating theapparatus of FIG. 30 in a second condition following implantation in thevertebrae;

FIG. 37 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a fifth embodiment of the presentinvention;

FIG. 38 is a sectional view taken along line 38—38 in FIG. 37;

FIG. 39 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a sixth embodiment of the presentinvention;

FIG. 40 is a sectional view taken along line 40—40 in FIG. 39;

FIG. 41 is a sectional view taken along line 41—41 in FIG. 39;

FIG. 42 is a sectional view taken along line 42—42 in FIG. 39;

FIG. 43 is a schematic side view of an apparatus for correcting spinaldeformity in accordance with a seventh embodiment of the presentinvention;

FIG. 44 is a sectional view taken along line 44—44 in FIG. 43;

FIG. 45 is an exploded perspective view of the apparatus of FIG. 43, andalso illustrates a driver for rotating the apparatus; and

FIG. 46 is a schematic anterior view illustrating the apparatus of FIG.43 implanted in a vertebrae.

DESCRIPTION OF EMBODIMENTS

The present invention is directed to a method and apparatus 10 forcorrecting spinal deformity, such as scoliosis, kyphosis, and/orlordosis. As illustrated in FIG. 1, the apparatus 10 includes an anchor20 for implanting in a vertebrae 12 (FIG. 6). The anchor 20 is made froma biocompatible material, such as titanium or stainless steel. It iscontemplated that the biocompatible material used for the anchor 20could also be polymeric or composite (i.e., carbon fiber or otherbiologic composite) in nature.

The anchor 20 is centered about a longitudinal axis 22 (FIG. 1). Theanchor 20 includes a platform 24 having a cylindrical outer surface 26extending between oppositely disposed first and second axial ends 28 and30 of the platform. The platform 24 includes a generally rectangularslot 32 that extends axially from the first end 28 toward the second end30 of the platform. Adjacent the first end 28, the platform 24 includesfirst and second segments of external threads 34 and 36 that areseparated by the slot 32. The slot 32 and the threads 34 and 36 providestructure for connecting spinal fixation instrumentation to the platform24 as discussed further below.

The platform 24 further includes a tunnel 40 and a plurality of parallelpassages 44 extending through the platform. As best seen in FIG. 2, thetunnel 40 extends transverse to and through the axis 22. The tunnel 40has an elliptical shape in cross-section. Each of the passages 44extends transverse to the tunnel 40 and intersects the tunnel. In theillustrated embodiment, a centrally located first passage 45 extendsthrough the axis 22. Second and third passages 46 and 47 are located oneither side of the centrally located first passage 45. It should beunderstood that the platform 24 could have more or less than threepassages 44.

The second end 30 of the platform 24 includes an end surface 38 having aconvex shape that is complimentary to the shape of a concave sidesurface 14 (FIG. 6) on the vertebrae 12. It should be understood thatthe end surface 38 of the platform 24 could be any shape necessary toremain complimentary to the shape of the side surface 14 of thevertebrae 12. The end surface 38 of the platform 24 may include barbs(not shown) or other suitable structure for fixedly engaging the sidesurface 14 of the vertebrae 12. Further the end surface 38 of theplatform 24 may also be porous, pitted, or have a biocompatible surfacecoating to assist with fixation of the anchor 20 to the vertebrae 12.

First and second helical spikes 50 and 52 project tangentially from theend surface 38 of the platform 24. The helical spikes 50 and 52 resemblea pair of intertwined corkscrews. As shown in FIGS. 3 and 4, each of thehelical spikes 50 and 52 has a solid cross-section. Alternatively, eachof the helical spikes 50 and 52 could have a tubular cross-section, asillustrated in FIGS. 3A and 4A, which provides a means for matching themodulus of elasticity of the bone. It is contemplated that, with atubular cross-section, the wall thickness can be varied/selected tomatch the modulus of elasticity of the bone, which can improve fixationstrength and load-sharing characteristics of the anchor 20 and the bone.

The first and second helical spikes 50 and 52 extend around the axis 22.The spikes 50 and 52 extend in a helical pattern about the axis 22 atthe same, constant radius R1. It is contemplated, however, that thefirst and second helical spikes 50 and 52 could extend about the axis 22at different radiuses. Further, it is contemplated that the radius ofone or both of the first and second helical spikes 50 and 52 couldincrease or decrease as the helical spikes extend away from the platform24.

In the illustrated embodiment, the first and second helical spikes 50and 52 have the same axial length, and also have the same circularcross-sectional shape. It is contemplated, however, that the first andsecond helical spikes 50 and 52 could have different axial lengths.Further, it is contemplated that the helical spikes 50 and 52 could havea different cross-sectional shape, such as an oval shape. It alsocontemplated that the first and second helical spikes 50 and 52 couldhave different cross-sectional areas (i.e., one spike being thicker thanthe other spike). Finally, it is contemplated that the helical spikes 50and 52 should have the same pitch, and that the pitch of the helicalspikes would be selected based on the specific surgical application andquality of the bone in which the anchor 20 is to be implanted.

Each of the first and second helical spikes 50 and 52 can be dividedinto three portions: a connecting portion 54, an intermediate portion56, and a tip portion 58. The connecting portion 54 of each of thehelical spikes 50 and 52 is located at a proximal end 60 that adjoinsthe end surface 38 of the platform 24. The connection portion 54 mayinclude barbs (not shown) for resisting pull-out of the helical spikes50 and 52 from the vertebrae 12. According to one method formanufacturing the anchor 20, the connecting portion 54 of each of thehelical spikes 50 and 52 is fixedly attached to the platform 24 byinserting, in a tangential direction, the proximal ends 60 of thehelical spikes into openings (not shown) in the end surface 38 andwelding the connecting portions 54 to the platform. The insertedproximal ends 60 of the helical spikes 50 and 52 help to reduce bendingstresses on the helical spikes under tensile or shear loads.

Alternatively, the helical spikes 50 and 52 may be formed integrallywith the platform 24, such as by casting the anchor 20. If the anchor 20is cast, it is contemplated that a fillet (not shown) may be added atthe junction of the helical spikes 50 and 52 and the platform 24 tostrengthen the junction and minimize stress concentrations at theconnecting portions 54. The fillet at the junction of the helical spikes50 and 52 and the platform 24 also helps to reduce bending stresses inthe connection portions 54 of the helical spikes under tensile or shearloads.

As best seen in FIG. 2, the connecting portions 54 at the proximal ends60 of the first and second helical spikes 50 and 52 are spaced 180°apart about the axis 22 to balance the anchor 20 and evenly distributeloads on the helical spikes. The tip portion 58 of each of the helicalspikes 50 and 52 is located at a distal end 62 of the helical spikes.The intermediate portion 56 of each of the helical spikes 50 and 52extends between the tip portion 58 and the connecting portion 54.

The tip portion 58 of each of the helical spikes 50 and 52 has anelongated conical shape with a sharp pointed tip 64 (FIG. 1) forpenetrating into the vertebrae 12 as the platform 24 of the anchor 20 isrotated in a clockwise direction. FIG. 7 illustrates an alternative,self-tapping configuration for the tip portions 58 which includes aplanar surface 66 for driving into the vertebrae 12, in the same mannerthat a wood chisel turned upside-down drives into wood, as the platform24 is rotated. It is contemplated that the tip portions 58 could alsohave a pyramid shape (not shown), similar to the tip of a nail.

Although the outer surfaces of the helical spikes 50 and 52 are shown asbeing smooth, it is contemplated that the outer surfaces may instead beporous, pitted, or have a biocompatible coating to assist with fixationof the anchor 20 to the vertebrae 12.

It is further contemplated that the tip portions 58 of the helicalspikes 50 and 52 could be covered with tip protectors (not shown) toprevent accidental sticks to surgical staff and accidental damage totissue surrounding the vertebrae. Such tip protectors could be made of abio-absorbable material, such as polylactic acid, or non-bio-absorbablematerial, such as medical grade silicon. The tip protectors would bemanually removed or pushed-off during implantation of the anchor 20.

The apparatus 10 for correcting spinal deformity further includes aremovable rod 70 (FIG. 5), a bar 100, a lock nut 102, and a braidedcable 120 (FIG. 8). Optionally, the apparatus 10 may also include aremovable pin or dowel 80 (FIG. 5). The removable rod 70 has anelliptical cross-section and is dimensioned to fit into the tunnel 70 inthe platform 24 on the anchor 20. The rod 70 includes a plurality ofopenings 72 that extend radially through the rod and which are designedto be alignable with one or more of the passages 44 in the platform 24of the anchor 20.

The cable 120 (FIG. 8) has oppositely disposed first and second ends.The first end of the cable 120 tapers to a blunt point (not shown). Thesecond end of the cable 120 has a fixed or permanent crimp 122. As isdescribed in detail below, the cable 120 is used to straighten curvaturein the spine prior to attachment of the bar 100 to the anchor 20.

To implant the anchor 20, a tool (not shown) is used to punch two holes(not shown) in the cortical bone (not shown) of the vertebrae 12. Theholes are punched in locations that correspond to the spacing of the tipportions 58 of the helical spikes 50 and 52 on the anchor 20. It shouldbe noted that one or both of the configurations of the tip portions 58illustrated in FIGS. 1-7 may be able to punch through the cortical boneupon rotation of the anchor 20, thus eliminating the need for theaforementioned tool to punch holes in the cortical bone.

The tip portions 58 are then placed in the holes in the vertebrae 12 anda rotatable driver 130 (FIG. 5) is inserted into the slot 32 in theplatform 24. The driver 130 is then rotated, causing the anchor 20 torotate as well. It is contemplated that a cylindrical sleeve (not shown)may be placed around the intermediate portions 56 and the connectingportions 54 of the helical spikes 50 and 52 to prevent the helicalspikes from deforming radially outward during the initial rotation ofthe anchor 20.

Rotation of the anchor 20 screws the helical spikes 50 and 52 into thecancellous bone of the vertebrae 12. The tangentially-orientedconnection between the connecting portions 54 of the helical spikes 50and 52 and the platform 24 minimizes bending loads on the connectingportions during rotation of the anchor 20. Further, thetangentially-oriented connection ensures that the force vector resultingfrom torque and axial force applied by the driver 130 to platform 24 istransmitted along the helical centerline (not shown) of each of thehelical spikes 50 and 52.

As the anchor 20 is rotated, the tip portion 58 of the first helicalspike 50 penetrates the cancellous bone and cuts a first helical tunnel84 (FIG. 6) through the vertebrae 12. Simultaneously, the tip portion 58of the second helical spike 52 penetrates the cancellous bone of thevertebrae 12 and cuts a second helical tunnel 86. The first and secondhelical tunnels 84 and 86 are shaped like the helical spikes 50 and 52,respectively. Continued rotation of the anchor 20 embeds the helicalspikes 50 and 52 deeper into the cancellous bone of the vertebrae 12.The anchor 20 is rotated until the convex end surface 38 of the platform24 seats against the concave side surface 14 of the vertebrae 12 asshown in FIG. 6.

FIGS. 8-11 illustrate how the apparatus 10 is used to correct spinaldeformity. Thoracic vertebrae T5-T7, indicated by reference numbers 90,91, and 92, respectively, exhibit thoracic kyphosis. Because of thekyphosis in the spine, the anchors 20 implanted in the vertebrae 90-92do not line up straight in the sagittal plane. After gaining access tothe site either anteriorly or posteriorly, each of the vertebrae 90-92are implanted with the anchor 20 according to the present invention asdescribed above. Next, all disk material 94 (shown schematically inFIGS. 8-11) that normally separates each of the vertebrae 90-92 isremoved.

The removable rod 70 associated with each of the anchors 20 is theninserted into the tunnel 40 in the platform 24 of each of the anchors.Each of the rods 70 is inserted to a depth in the tunnel 40 determinedby the surgeon based on the amount of physical space available and, asexplained further below, the length of the lever arm needed duringcorrection of the spinal deformity. Although FIG. 8 shows each of therods 70 being inserted to the same depth, this is not a requirement. Itis required, however, that each rod 70 be inserted to a depth in thetunnel 40 so that at least one of the openings 72 in the rod aligns withone of the passages 44 in the platform. When one of the openings 72 ineach of the rods 70 is aligned with one of the passages 44 in theplatform 24, such as the central passage 45 as shown in FIG. 8, thedowel 80 is pressed into the aligned passage and corresponding openingto connect the removable rod 70 to the anchor 20. This process ofconnecting the dowel 80 to the anchor 20 is repeated for each of theanchors that have been implanted.

The cable 120 is then passed through one of the openings 72 in each ofthe removable rods 70, as shown in FIG. 8, with the surgeon decidingwhich of the openings in each rod to pass the cable through. If thesurgeon decides to pass the cable 120 through one of the openings 72that lies near the platform 24, when the cable is tightened, the leverarm formed by the rod 70 will be shorter than if the cable were passedthrough the opening in the rod that lies farthest away from theplatform. Since a longer lever arm will apply more force on the anchor20, the surgeon can select which of the openings 72 in each of the rods70 to use based on the amount of force needed to achieve the desiredmovement of each of the vertebrae in which the anchors are implanted.

By way of example, in FIG. 8, the cable 120 is threaded first throughone of the openings 72 in the rod 70 connected to the anchor 20 that isimplanted in the upper (as viewed in the FIGS. 8-11) vertebrae 90. Next,the cable 120 is threaded through one of the openings 72 in the rod 70connected to the anchor 20 implanted in the middle (as viewed in theFIGS. 8-11) vertebrae 91. Finally, the cable 120 is threaded through oneof the openings 72 in the rod 70 connected to the anchor 20 that isimplanted in the lower (as viewed in the FIGS. 8-11) vertebrae 92. Asbest seen in FIG. 8, because of the kyphosis, the cable 120 initiallyhas a curved configuration.

The first end of the cable 120 is then pulled tight so that the crimp122 on the second end of the cable engages the rod 70 connected to theanchor 20 in the upper vertebrae 90. Tension is then applied to thecable 120 in the direction of arrow A in FIG. 8 using a cable tensioningdevice (not shown). The tension in the cable 120 causes the cable tostraighten. As the cable 120 straightens, the middle vertebrae 91 isrotated, in the direction of arrow B, with respect to the upper andlower vertebrae 90 and 92. The rotation of the middle vertebrae 91 movesthe middle vertebrae into an aligned, corrected position with respect tothe upper and lower vertebrae 90 and 92, as may be seen in FIG. 9.

Once the vertebrae 90-92 are in the positions shown in FIG. 9, the bar100 is placed into the slot 32 in each of the anchors 20. Tension ismaintained in the cable 120 until the nuts 102 are screwed onto thethreads 34 and 36 on each of the platforms 24 to secure the bar 100 toeach of the anchors 20 (FIGS. 10 and 11). With the bar 100 secured inplace, the cable 120, the dowels 80, and the rods 70 are removed.Finally, the spaces left between the vertebrae 90-92 are filled withbone graft material 96 (shown schematically in FIGS. 10 and 11) thatfuses the vertebrae together over time.

When implanted, the anchors 20 can be subjected to substantial forcescaused by human body movement and muscle memory. In some cases, theseforces can tend to pull the conventionally designed screws out of thevertebrae 90-92, and can also cause such screws to toggle in thevertebrae. However, when the helical spikes 50 and 52 of the anchors 20are embedded in the vertebrae 90-92, the twin helical spikes of theanchors 20 provide the anchors with a high resistance to pull-outforces. Preliminary cadaver testing indicates that the anchor 20 is soresistant to being pulled axially from a vertebral body that thevertebral body itself is likely to fail before the anchor pulls outunder high tensile load. Further, the helical spikes 50 and 52, andtheir tangential connection with the platform 24, provide the anchors 20with a high resistance to toggling in the vertebrae 90-92.

Because the helical spikes 50 and 52 of the anchor 20 displace much lessof the cancellous bone of a vertebrae during implantation than aconventional solid shank bone screw, much less torque is required toimplant the anchor in a vertebrae than is required by a conventionalbone screw. Finally, because the helical spikes 50 and 52 displace onlya small amount of bone, the helical spikes do not create a core defectthat could lead to bone deformation or failure, such as the helicalspikes pulling out of the vertebrae.

FIGS. 12-16 illustrate the thoracic vertebrae 90-92 in a spine havingmultiple deformities, such as scoliosis and kyphosis. In accordance withanother feature of the present invention, such a condition may becorrected using the apparatus 10 described above in conjunction withadditional structure in the form of a secondary cable 150 (FIG. 15). InFIGS. 12-16, reference numbers that are the same as those used in FIGS.1-11 designate parts that are the same as parts in FIGS. 1-11.

As shown in FIG. 12, the thoracic vertebrae 90-92 exhibit curvature inthe coronal plane indicative of scoliosis. In order to correct thescoliosis, the anchors 20 are implanted in the vertebrae 90-92 asdescribed above, and all disk material 94 (shown schematically in theFigures) between the vertebrae 90-92 is removed.

The removable rod 70 associated with each of the anchors 20 is theninserted into the tunnel 40 in the platform 24 of each of the anchors.Each of the rods 70 is inserted to a depth in the tunnel 40 determinedby the surgeon based on the amount of physical space available and thelength of the lever arm required during correction of the spinaldeformity. Although FIG. 14 shows each of the rods 70 being inserted tothe same depth, this is not a requirement. It is required, however, thateach rod 70 be inserted to a depth in the tunnel 40 so that at least oneof the openings 72 in the rod aligns with one of the passages 44 in theplatform. When one of the openings 72 in each of the rods 70 is alignedwith one of the passages 44 in the platform 24, such as the centralpassage 45 as shown in FIG. 14, the cable 120 is then used to connecteach of the rods 70 to the anchors 20.

The cable 120 is inserted into the central passage 45 in each of theanchors 20 and passed through the opening 72 in each of the removablerods 70 that is aligned with the central passage, as shown in FIG. 14.The first end of the cable 120 is then pulled tight so that the crimp122 on the second end of the cable engages the platform 24 of the anchor20 in the upper vertebrae 90. Tension is then applied to the cable 120in the direction of arrow C in FIG. 13. The tension in the cable 120causes the cable to straighten. As the cable 120 straightens, thevertebrae 90-92 are moved into an aligned, corrected position shown inFIGS. 13 and 14. A locking clamp or crimp 124 is then placed on thecable 120 at the junction of the cable and the anchor 20 in the lowervertebrae 92, thereby securing the cable to the anchors. The cable 120also functions to establish a connection between the each of theremovable rods 70 and a respective one of the anchors 20. Further,securing the cable 120 between the anchors 20 establishes a pivot pointin the sagittal plane for movement of the vertebrae 90-92 to correct thekyphosis.

Next, as shown in FIG. 15, the secondary cable 150 is then passedthrough one of the openings 72 in each of the removable rods 70, withthe surgeon deciding which of the openings in each rod to pass the cablethrough. If the surgeon decides to pass the cable 150 through one of theopenings 72 that lies near the platform 24, when the cable is tightened,the lever arm formed by the rod 70 will be shorter than if the cablewere passed through the opening in the rod that lies farthest away fromthe platform. Since a longer lever arm will apply more force on theanchor 20, the surgeon can select which of the openings 72 in each ofthe rods 70 to use based on the amount of force needed to achieve thedesired movement of each of the vertebrae in which the anchors areimplanted.

In FIG. 15, the secondary cable 150 is threaded first through one of theopenings 72 in the rod 70 connected to the anchor 20 that is implantedin the upper (as viewed in the FIGS. 8-11) vertebrae 90. Next, thesecondary cable 150 is threaded through one of the openings 72 in therod 70 connected to the anchor 20 implanted in the middle (as viewed inthe FIGS. 8-11) vertebrae 91. Finally, the secondary cable 150 isthreaded through one of the openings 72 in the rod 70 connected to theanchor 20 that is implanted in the lower (as viewed in the FIGS. 8-11)vertebrae 92. Because of the kyphosis, the secondary cable 150 initiallyhas a curved configuration.

The end of the secondary cable 150 is then pulled tight so that a crimp152 on the other end of the secondary cable engages the rod 70 attachedto the anchor 20 in the upper vertebrae 90, as shown in FIG. 16. Tensionis then applied to the secondary cable 150 in the direction of arrow Din FIG. 16. The tension in the secondary cable 150 causes the secondarycable to straighten. As the secondary cable 150 straightens, thevertebrae 90-92 are moved, about the pivot plane formed by the cable120, into an aligned, corrected position, as may be seen in FIG. 16.

Once the vertebrae 90-92 are in the positions shown in FIG. 16, the bar100 (FIG. 17) is placed into the slot 32 in each of the anchors 20.Tension is maintained in the secondary cable 150 until the nuts 102 arescrewed onto the threads 34 and 36 on each of the platforms 24 to securethe bar 100 to each of the anchors 20. With the bar 100 secured inplace, the cables 120 and 150 and the rods 70 are removed. Finally, thespaces left between the vertebrae 90-92 are filled with the bone graftmaterial 96 that fuses the vertebrae together over time.

FIGS. 18-23 illustrate several lumbar vertebrae in a spine havingmultiple deformities, such as scoliosis and lordosis. In accordance withanother feature of the present invention, such a condition may becorrected using the apparatus 10 described above in conjunction withadditional structure in the form of a secondary cable 170 (FIG. 21). InFIGS. 18-23, reference numbers that are the same as those used in FIGS.1-17 designate parts that are the same as parts in FIGS. 1-17.

As shown in FIG. 18, three lumbar vertebrae 190, 191, and 192 exhibitcurvature in the coronal plane indicative of scoliosis. In order tocorrect the scoliosis, the anchors 20 are implanted in the vertebrae190-192 as described above and all disk material 94 (shown schematicallyin the Figures) between the vertebrae is removed.

The removable rod 70 associated with each of the anchors 20 is theninserted into the tunnel 40 in the platform 24 of each of the anchors.Each of the rods 70 is inserted to a depth in the tunnel 40 determinedby the surgeon based on the amount of physical space available and thelength of the lever arm required during correction of the spinaldeformity. Although FIG. 20 shows each of the rods 70 being inserted tothe same depth, this is not a requirement. It is required, however, thateach rod 70 be inserted to a depth in the tunnel 40 so that at least oneof the openings 72 in the rod aligns with one of the passages 44 in theplatform. When one of the openings 72 in each of the rods 70 is alignedwith one of the passages 44 in the platform 24, such as the centralpassage 45 as shown in FIG. 20, the cable 120 is then used to connecteach of the rods 70 to the anchors 20.

The cable 120 is inserted into the central passage 45 in each of theanchors 20 and passed through the opening 72 in each of the removablerods 70 that is aligned with the central passage, as shown in FIG. 20.The first end of the cable 120 is then pulled tight so that the crimp122 on the second end of the cable engages the platform 24 of the anchor20 in the upper vertebrae 190. Tension is then applied to the cable 120in the direction of arrow E in FIG. 20. The tension in the cable 120causes the cable to straighten. As the cable 120 straightens, thevertebrae 190-192 are moved into an aligned, corrected position shown inFIG. 19. A locking clamp or crimp 124 is then placed on the cable 120 atthe junction of the cable and the anchor 20 in the lower vertebrae 192,thereby securing the cable to the anchors. The cable 120 also functionsto establish a connection between the each of the removable rods 70 anda respective one of the anchors 20. Further, securing the cable 120between the anchors 20 establishes a pivot point in the sagittal planefor movement of the vertebrae 190-192 to correct the lordosis.

Next, as shown in FIG. 21, the secondary cable 170 is then passedthrough one of the openings 72 in each of the removable rods 70, withthe surgeon deciding which of the openings in each rod to pass the cablethrough. If the surgeon decides to pass the cable 170 through one of theopenings 72 that lies near the platform 24, when the cable is tightened,the lever arm formed by the rod 70 will be shorter than if the cablewere passed through the opening in the rod that lies farthest away fromthe platform. Since a longer lever arm will apply more force on theanchor 20, the surgeon can select which of the openings 72 in each ofthe rods 70 to use based on the amount of force needed to achieve thedesired movement of each of the vertebrae in which the anchors areimplanted.

In FIG. 21, the secondary cable 170 is threaded first through one of theopenings 72 in the rod 70 connected to the anchor 20 that is implantedin the upper (as viewed in the FIGS. 8-11) vertebrae 190. Next, thesecondary cable 170 is threaded through one of the openings 72 in therod 70 connected to the anchor 20 implanted in the middle (as viewed inthe FIGS. 8-11) vertebrae 191. Finally, the secondary cable 170 isthreaded through one of the openings 72 in the rod 70 connected to theanchor 20 that is implanted in the lower (as viewed in the FIGS. 8-11)vertebrae 192. Because of the lordosis, the secondary cable 170initially has a curved configuration.

The free end of the secondary cable 170 is then pulled tight so that acrimp 152 on the other end of the secondary cable engages the rod 70attached to the anchor 20 in the upper vertebrae 190, as shown in FIG.16. Tension is then applied to the secondary cable 170 in the directionof arrow D in FIG. 16. The tension in the secondary cable 170 causes thesecondary cable to straighten. As the secondary cable 170 straightens,the vertebrae 190-192 are moved, about the pivot plane formed by thecable 120, into an aligned, corrected position, as may be seen in FIG.22.

Once the vertebrae 190-192 are in the positions shown in FIG. 22, thebar 100 (FIG. 23) is placed into the slot 32 in each of the anchors 20.Tension is maintained in the secondary cable 170 until the nuts 102 arescrewed onto the threads 34 and 36 on each of the platforms 24 to securethe bar 100 to each of the anchors 20. With the bar 100 secured inplace, the cables 120 and 170 and the rods 70 are removed. Finally, thespaces left between the vertebrae 90-92 are filled with the bone graftmaterial 96 that fuses the vertebrae together over time.

FIGS. 24-27 illustrate an apparatus 210 constructed in accordance with asecond embodiment of the present invention. In the second embodiment ofFIGS. 24-27, reference numbers that are the same as those used in FIGS.1-6 designate parts that are the same as parts shown in FIGS. 1-6.

According to the second embodiment, the apparatus 210 comprises ananchor 220 having helical spikes 50′ and 52′. FIGS. 24-27 illustratethat the connecting portions 54 and the tip portions 58 of the helicalspikes 50′ and 52′ have a solid cross-section, while the intermediateportions 56 have a tubular cross-section. The modified configuration ofthe anchor 220 provides additional means for matching the modulus ofelasticity of the bone.

The anchor 220 is implantable into vertebrae in the same manner as theanchor 20 described above. Once implanted, the anchor 220 may be usedalong with the rods 70, one or more of the cables 120, 150 and 170, thebar 100, and the nuts 102 described above to achieve and maintaincorrection of spinal deformity.

FIGS. 28 and 29 illustrate an apparatus 310 constructed in accordancewith a third embodiment of the present invention. In the thirdembodiment of FIGS. 28 and 29, reference numbers that are the same asthose used in FIGS. 1-6 designate parts that are the same as parts shownin FIGS. 1-6.

According to the third embodiment, the apparatus 310 comprises an anchor320 having three helical spikes 330, 331, and 332 projectingtangentially from the end surface 38 of the platform 24. The spikes330-332 extend around the axis 22. As shown in FIGS. 28 and 29, each ofthe helical spikes 330-332 has a solid cross-section. Alternatively,each of the helical spikes 330-332 could have a tubular cross-section,which provides a means for matching the modulus of elasticity of thebone.

As shown in FIG. 29, the connecting portions 54 at the proximal ends 60of the helical spikes 330-332 are spaced 120° apart about the axis 22,which balances the anchor 320 and evenly distributes loads on thehelical spikes. Each of the three helical spikes 330-332 extends in ahelical pattern about the axis 22 at the same, constant radius R1. It iscontemplated, however, that one or more of the helical spikes 330-332could extend about the axis 22 at different radiuses. Further, it iscontemplated that the radius of one or more helical spikes 330-332 couldincrease or decrease as the helical spikes extend away from the platform24.

The three helical spikes 330-332 have the same axial length and alsohave the same circular cross-sectional shape. It is contemplated,however, that one or more of the helical spikes 330-332 could havedifferent axial lengths. Further, it is contemplated that one or more ofthe helical spikes 330-332 could have a different cross-sectional shape,such as an oval shape. It also contemplated that the one or more of thehelical spikes 330-332 could have different cross-sectional areas (i.e.,one spike being thicker or thinner than the other two spikes). Finally,it is contemplated that the helical spikes 330-332 should have the samepitch, and that the pitch of the helical spikes would be selected basedon the specific surgical application and quality of the bone in whichthe anchor 20 is to be implanted.

It is contemplated that the modified configuration of the helical spikes50′ and 52′ illustrated in the second embodiment of FIGS. 24-27 couldalso be applied to the third embodiment of FIGS. 28 and 29.Specifically, the connecting portions 54 and/or the tip portions 58 ofthe helical spikes 330-332 could have a solid cross-section, while theintermediate portions 56 have a tubular cross-section. Such modifiedconfigurations of the anchor 320 provide additional means for matchingthe modulus of elasticity of the bone and allow the surgeon to select aparticular configuration based on the specific signal application andquality of the bone in which the anchor is to be implanted.

The tip portion 58 of each of the helical spikes 330-332 illustrated inFIG. 28 has an elongated conical shape for penetrating into a vertebraeas the platform 24 of the anchor 320 is rotated in the clockwisedirection. It should be understood that the tip portions 58 of thehelical spikes 330-332 of the anchor 320 could alternatively beconfigured like the tip portions illustrated in FIG. 7.

It is further contemplated that the tip portions 58 of the helicalspikes 330-332 could be covered with tip protectors (not shown) toprevent accidental sticks to surgical staff and accidental damage totissue surrounding the fractured bone. Such tip protectors could be madeof a bio-absorbable material, such as polylactic acid or anon-bio-absorbable material, such as medical grade silicon. The tipprotectors would be manually removed or pushed-off during implantationof the anchor 320.

The anchor 320 according to the third embodiment of FIGS. 28 and 29 isimplanted in a vertebrae in the same manner as the anchor 20 accordingto the first embodiment of FIGS. 1-6. Because the helical spikes 330-332of the anchor 320 displace less cancellous bone during implantation thana conventional solid shank bone screw, less torque is required toimplant the anchor in a vertebrae than is required by a conventionalbone screw. Further, because the helical spikes 330-332 displace only asmall amount of bone, the helical spikes do not create a core defectthat could lead to bone destruction or failure, such as the helicalspikes pulling out of the vertebrae. Finally, when implanted, the anchor320 is highly resistant to being pulled out of the vertebrae and totoggling in the vertebrae despite being subjected to substantial forcescaused by human body movement and muscle memory.

Once the anchor 320 is implanted into a vertebrae in the mannerdescribed above with regard to the first embodiment, the anchor 320 maybe used along with the rods 70, one or more of the cables 120, 150 and170, the bar 100, and the nuts 102 described above to achieve andmaintain correction of spinal deformity.

FIGS. 30-36 illustrate an apparatus 410 constructed in accordance with afourth embodiment of the present invention. In the fourth embodiment ofFIGS. 30-36, reference numbers that are the same as those used in FIGS.1-6 designate parts that are the same as parts shown in FIGS. 1-6.

According to the fourth embodiment, the apparatus 410 comprises ananchor 420 made from a biocompatible material. Known biocompatiblematerials include titanium, stainless steel, and spring steel. It iscontemplated that the biocompatible material used for the anchor 420could be polymeric or composite in nature. In accordance with onefeature of the present invention, the anchor 420 is at least partiallymade from a shape memory alloy that is biocompatible. As is known in theart, shape memory alloys have the ability to return to a predeterminedshape when heated. When a shape memory alloy is cold, or below itstransition temperature range (TTR), the material has a low yieldstrength and can be deformed into a new shape, which it will retainuntil heated. However, when a shape memory alloy is heated above itsTTR, the material undergoes a change in crystal structure (from amartensite structure to an austensite structure), which causes thematerial to return to its original, or “memorized” shape. A memorizedshape is imprinted into a shape memory alloy by first holding thematerial in the desired shape at a high temperature, and then continuingto hold the material in the desired shape as it cools through its TTR.

As shown in FIG. 30, the anchor 420 is centered about a longitudinalaxis 422. The anchor 420 includes the platform 24 described above withregard to FIGS. 1-6. First and second helical spikes 450 and 452 projecttangentially from the end surface 38 of the platform 24. The helicalspikes 450 and 452 resemble a pair of intertwined corkscrews, both ofwhich have a conical shape that increases in diameter as the helicalspikes extend away from the platform 24. As shown in FIGS. 32 and 33,each of the helical spikes 450 and 452 has a solid cross-section.Alternatively, each of the helical spikes 450 and 452 could have atubular cross-section, as illustrated in FIGS. 32A and 33A, whichprovides a means for matching the modulus of elasticity of the bone.

According to the fourth embodiment illustrated in FIGS. 30-36, the firstand second helical spikes 450 and 452 extend symmetrically in a conicalpattern about the axis 422. It is contemplated, however, that theconical shape of the first and second helical spikes 450 and 452 couldbe different from each other (i.e., one spike being a smaller cone thanthe other spike).

As shown in FIGS. 30-36, the first and second helical spikes 450 and 452have the same axial length, and also have the same cross-sectionalshape. It is contemplated, however, that the first and second helicalspikes 450 and 452 could have different axial lengths. Further, it iscontemplated that the helical spikes 450 and 452 could have a differentcross-sectional shape, such as an oval shape. It also contemplated thatthe first and second helical spikes 450 and 452 could have differentdiameters (i.e., one spike being thicker than the other spike). Finally,it is contemplated that the helical spikes 450 and 452 should have thesame pitch, and that the pitch of the helical spikes would be selectedbased on the specific surgical application and quality of the bone inwhich the anchor 420 is to be implanted.

Each of the first and second helical spikes 450 and 452 can be dividedinto three portions: a connecting portion 454, an intermediate portion456, and a tip portion 458. The connecting portion 454 of each of thehelical spikes 450 and 452 is located at a proximal end 460 that adjoinsthe end surface 38 of the platform 24. The connecting portion 454 mayinclude barbs (not shown) for resisting pull-out of the helical spikes450 and 452 from a vertebrae. According to one method for manufacturingthe anchor 420, the connecting portion 454 of each of the helical spikes450 and 452 is fixedly attached to the platform 24 by inserting, in atangential direction, the proximal ends 460 of the helical spikes intoopenings (not shown) in the end surface 38 and welding the connectingportions 454 to the platform. The inserted proximal ends 460 of thehelical spikes 450 and 452 help to reduce bending stresses on thehelical spikes under tensile or shear loads.

Alternatively, the helical spikes 450 and 452 may be formed integrallywith the platform 24, such as by casting the anchor 420. If the anchor420 is cast, it is contemplated that a fillet (not shown) may be addedat the junction of the helical spikes 450 and 452 and the platform 24 tostrengthen the junction and minimize stress concentrations at theconnecting portions 454. The fillet at the junction of the helicalspikes 450 and 452 and the platform 24 also helps to reduce bendingstresses in the connection portions 454 of the helical spikes undertensile or shear loads. As best seen in FIG. 31, the connecting portions454 at the proximal ends 460 of the first and second helical spikes 450and 452 are spaced 180° apart about the axis 422 to balance the anchor420 and evenly distribute loads on the helical spikes.

The tip portion 458 of each of the helical spikes 450 and 452 is locatedat a distal end 462 of the helical spikes. The intermediate portion 456of each of the helical spikes 450 and 452 extends between the tipportion 458 and the connecting portion 454. The intermediate portion 456and the tip portion 458 of each of the helical spikes 450 and 452 have adiameter that is less than or equal to the diameter of the connectingportions 454. If the diameter of the intermediate portion 456 and thetip portion 458 is less than the diameter of the connecting portion 454of each of the helical spikes 450 and 452, the increased thickness ofthe connecting portions will help to provide the anchor 420 withincreased tensile strength at the junction of the helical spikes and theplatform 24.

The tip portion 458 of each of the helical spikes 450 and 452 has anelongated conical shape with a sharp pointed tip 468 for penetratinginto a vertebrae as the platform 24 of the anchor 420 is rotated in aclockwise direction. It should be understood that the tip portions 458could alternatively have the configuration shown in FIG. 7. It iscontemplated that the tip portions 458 could also have a pyramid shape(not shown), similar to the tip of a nail. Although the outer surfacesof the helical spikes 450 and 452 are shown as being relatively smoothin FIGS. 30-36, it is contemplated that the outer surfaces may insteadbe porous, pitted, or have a biocompatible coating to assist withfixation of the anchor 420 to a vertebrae.

As mentioned previously, the anchor 420 is made from a shape memoryalloy, which allows the anchor to have more than one shape. FIGS. 34-36illustrate the shapes of the anchor 420 at various stages of theimplantation process. The shape that is “memorized” into the material ofthe anchor 420 is illustrated in FIGS. 30 and 36. FIG. 34 illustratesthe anchor 420 in a first condition prior to implantation in a vertebrae412. In the first condition, the helical spikes 450 and 452 of theanchor 420 do not have a conical shape, but instead have a generallycylindrical shape with a uniform maximum diameter D1. Further, in thefirst condition, the helical spikes 450 and 452 have an axial length L1.In order for the anchor 420 to take the shape of the first condition,the temperature of the anchor must be below its TTR so that the materialof the anchor is soft and ductile.

The anchor 420 is moved into the first condition of FIG. 34 with the aidof tubular sleeve 470. The sleeve 470 is made from a hard metal andincludes internal threads 472 (FIG. 35) for mating with the helicalspikes 450 and 452 of the anchor 420 to aid in drawing the helicalspikes into the sleeve upon rotation of the anchor. With the temperatureof the anchor 420 below its TTR, the anchor is pulled into the sleeve470 by rotating the platform 24 in a first direction with a driver (notshown) that fits into the slot 432. As the helical spikes 450 and 452are drawn into the sleeve 470, the helical spikes are compressedradially inward, causing their axial length to grow to the axial lengthL1.

FIG. 35 illustrates the anchor 420 during implantation into thevertebrae 412. As shown in FIG. 35, the helical spikes 450 and 452emerge from the sleeve 470 when the platform 24 is rotated in a seconddirection that is opposite the first direction. As the helical spikes450 and 452 emerge from the sleeve 470, it is desired for the helicalspikes to return to the memorized conical shape of FIG. 30. To returnthe helical spikes 450 and 452 to the conical shape as they emerge fromthe sleeve 470, heat is applied to the anchor 420 until the temperatureof the anchor exceeds the TTR for the shape memory material. Simple bodytemperature may be sufficient to raise the temperature of the anchor 420above its TTR. If additional heat is needed, heat may be applied in manyways, such as passing electric current through a wire connected with theanchor 420 or the sleeve 470, transmitting radio waves that inductivelyheat the anchor, or applying a hot saline pack to the anchor.

With the helical spikes 450 and 452 expanding radially, but contractingaxially, as they emerge from the sleeve 470, the helical spikes areimplanted in the vertebrae 412 in the conical shape, or secondcondition, illustrated in FIG. 36. As shown in FIG. 36, in the implantedsecond condition, the helical spikes 450 and 452 have a maximum diameterD2 that is larger than the maximum diameter D1 of the helical spikes inthe first condition. Further, in the implanted second condition, thehelical spikes 450 and 452 have an axial length L2 that is smaller thanthe axial length of the helical spikes in the first condition.

It is contemplated that the first and second conditions of the helicalspikes 450 and 452 described above could be achieved even if onlycertain portions of the helical spikes were made from a shape memoryalloy. For example, it is contemplated that the tip portions 458 and theintermediate portions 456 of the helical spikes 450 and 452 could bemade from a shape memory alloy, while the connecting portions 454 aremade from another biocompatible metal. Further, it should be understoodthat if a shape memory material is not used at all in the helical spikes450 and 452 and a material such as spring steel is used instead, thehelical spikes would still be able to be compressed in to the firstcondition of FIG. 34, and expand into the second condition uponimplantation as shown in FIGS. 35 and 36.

The anchor 420 is implantable into vertebrae in the same manner as theanchor 20 described above with regard to FIGS. 1-6. When implanted, theanchor 420 can be subjected to substantial forces caused by human bodymovement and muscle memory. In some cases, these forces can tend to pullthe known screws used in such an application out of a vertebrae or cancause the screws to toggle in the vertebrae. However, when the helicalspikes 450 and 452 are embedded in a vertebrae, the conical shape of thetwo helical spikes of the anchors 420 provides the anchors with a highresistance to pull-out forces and a high resistance to toggling in thevertebrae. The conical shape of the helical spikes 450 and 452 increasesthe amount of surface area engaged by the anchor 420, distributes anyload on the anchor, and provides fixation over a larger volume of bone.Finally, the use of a shape memory alloy for the helical spikes 450 and452 allows the anchor 420 to have a smaller diameter prior toimplantation, which permits minimally invasive endoscopic surgerythrough a cannula, and a wider diameter when implanted.

Because the helical spikes 450 and 452 of the anchor 420 displace muchless of the cancellous bone of a vertebrae during implantation than aconventional solid shank bone screw, much less torque is required toimplant the anchor in the vertebrae than is required by a conventionalbone screw. Further, because the helical spikes 450 and 452 displaceonly a small amount of bone, the helical spikes do not create a coredefect that could lead to bone deformation or failure, such as thehelical spikes pulling out of the vertebrae. Advantageously, the conicalshape of the helical spikes 450 and 452 increases the amount of surfacearea engaged by the anchor 420, spreads any load on the anchor out overdifferent areas of the vertebrae 412, and provides fixation over alarger volume of bone. The aforementioned advantages of the conicalshape of the helical spikes 450 and 452 is especially helpful whenimplanting the anchor 420 in osteoporotic bone.

Once implanted, the anchor 420 may be used along with the rods 70, oneor more of the cables 120, 150 and 170, the bar 100, and the nuts 102described above to achieve and maintain correction of spinal deformity.

FIGS. 37 and 38 illustrate an apparatus 510 constructed in accordancewith a fifth embodiment of the present invention. In the fifthembodiment of FIGS. 37 and 38, reference numbers that are the same asthose used in the fourth embodiment of FIGS. 30-36 designate parts thatare the same as parts in the fourth embodiment.

According to the fifth embodiment, the apparatus 510 comprises an anchor520 having three helical spikes 530, 531, and 532 projectingtangentially from the end surface 38 of the platform 24. The spikes530-532 extend around the axis 422 and have a conical shape thatincreases in diameter as the helical spikes extend away from theplatform. As shown in FIGS. 37 and 38, each of the helical spikes530-532 has a solid cross-section. Alternatively, each of the helicalspikes 530-532 could have a tubular cross-section.

As shown in FIG. 37, the connecting portions 454 at the proximal ends460 of the helical spikes 530-532 are spaced 120° apart about the axis422, which balances the anchor 520 and evenly distributes loads on thehelical spikes. The three helical spikes 530-532 extend symmetrically ina conical pattern about the axis 422. It is contemplated, however, thatthe conical shape of one or more of the helical spikes 530-532 could bedifferent from the other(s) (i.e., one spike being a smaller cone thanthe others). As shown in FIG. 37, the three helical spikes 530-532 havethe same axial length and also have the same cross-sectional shape. Itis contemplated, however, that one or more of the helical spikes 530-532could have different axial lengths. Further, it is contemplated that oneor more of the helical spikes 530-532 could have a differentcross-sectional shape, such as an oval shape. It also contemplated thatthe one or more of the helical spikes 530-532 could have differentdiameters (i.e., one spike being thicker or thinner than the otherspike(s)). Finally, it is contemplated that the helical spikes 530-532should have the same pitch, and that the pitch of the helical spikeswould be selected based on the specific surgical application and qualityof the bone in which the anchor 520 is to be implanted.

The tip portion 458 of each of the helical spikes 530-532 illustrated inFIG. 37 has an elongated conical shape for penetrating into a vertebraeas the platform 24 of the anchor 520 is rotated in the clockwisedirection. It should be understood that the tip portions 458 of thehelical spikes 530-532 of the anchor 520 could alternatively beconfigured like the tip portions illustrated in FIG. 7. Further,although the outer surfaces of the helical spikes 530-532 are shown asbeing smooth in FIGS. 37 and 38, it is contemplated that the outersurfaces may instead be porous, pitted, or have a biocompatible coatingto assist with fixation of the anchor 520 to the vertebrae.

The helical spikes 530-532 of the anchor 520 according to the secondembodiment of FIGS. 37 and 38 are also made of a shape memory alloy andare implanted in a vertebrae in the same manner as the anchor 420according to the fourth embodiment. The shapes of the anchor 520 atvarious stages of the implantation process are similar to that which isillustrated in FIGS. 34-36 for the anchor 420 of the fourth embodiment.Hence, the shape that is “memorized” into the material of the anchor 520is illustrated in FIG. 37. Further, the anchor 520 has a first condition(not shown) prior to implantation in a vertebrae in which the helicalspikes 530-532 do not have a conical shape, but instead have a generallycylindrical shape with a first maximum diameter. In addition, in thefirst condition, the helical spikes 530-532 have a first axial length.In order for the anchor 520 to take the shape of the first condition,the temperature of the anchor must be below its TTR so that the materialof the anchor is soft and ductile. As in the fourth embodiment of FIGS.30-36, the anchor 520 is also moved into the first condition with theaid of the tubular sleeve 470.

To return the helical spikes 530-532 to the conical shape as they emergefrom the sleeve 470, heat is applied to the anchor 520 until thetemperature of the anchor exceeds the TTR for the shape memory material.With the helical spikes 530-532 expanding radially and contractingaxially as they emerge from the sleeve 470, the helical spikes areimplanted in a vertebrae in the conical shape, or second condition, asillustrated in FIG. 36 for the fourth embodiment. In the implantedsecond condition, the helical spikes 530-532 have a second maximumdiameter that is larger than the first maximum diameter of the helicalspikes in the first condition. Further, in the implanted secondcondition, the helical spikes 530-532 have a second axial length that issmaller than the first axial length of the helical spikes in the firstcondition.

It is contemplated that the first and second conditions of the helicalspikes 530-532 described above could be achieved even if only certainportions of the helical spikes were made from a shape memory alloy. Forexample, it is contemplated that the tip portions 458 and theintermediate portions 456 of the helical spikes 530-532 could be madefrom a shape memory alloy, while the connecting portions 454 are madefrom another biocompatible metal. Further, if a shape memory material isnot used at all in the helical spikes 530-532 and a material such asspring steel is used instead, the helical spikes would still be able tobe compressed into the first condition and expand into the secondcondition upon implantation.

The anchor 520 is implantable into vertebrae in the same manner as theanchor 420 described above. Because the helical spikes 530-532 of theanchor 520 displace less cancellous bone during implantation than aconventional solid shank bone screw, less torque is required to implantthe anchor in a vertebrae than is required by a conventional bone screw.Further, the conical shape of the helical spikes 530-532 according tothe second embodiment, when implanted in a vertebrae, make the anchor520 highly resistant to being pulled out of the vertebrae and totoggling in the vertebrae despite being subjected to substantial forcescaused by human body movement and muscle memory. As mentionedpreviously, the conical shape of the helical spikes 530-532 increasesthe amount of surface area engaged by the anchor 420, distributes anyload on the anchor, and provides fixation over a larger volume volume ofbone. Finally, the use of a shape memory alloy for the helical spikes530-532 allows the anchor 520 to have a smaller diameter prior toimplantation, which permits minimally invasive endoscopic surgerythrough a cannula, and a wider diameter when implanted, which improvesfixation in a vertebrae.

Once implanted, the anchor 520 may be used along with the rods 70, oneor more of the cables 120, 150 and 170, the bar 100, and the nuts 102described above to achieve and maintain correction of spinal deformity.

FIGS. 39-42 illustrate an apparatus 610 constructed in accordance with asixth embodiment of the present invention. In the sixth embodiment ofFIGS. 39-42, reference numbers that are the same as those used in FIGS.30-36 designate parts that are the same as parts in FIGS. 30-36.

According to the sixth embodiment, the apparatus 610 comprises an anchor620 having helical spikes 450′ and 452′. FIGS. 39-42 illustrate that theconnecting portions 454 and the tip portions 458 of the helical spikes450′ and 452′ have a solid cross-section, while the intermediateportions 456 have a tubular cross-section. This configuration of theanchor 620 provides means for matching the modulus of elasticity of thebone.

The anchor 620 is implantable into vertebrae in the same manner as theanchor 420 described above. Once implanted, the anchor 620 may be usedalong with the rods 70, one or more of the cables 120, 150 and 170, thebar 100, and the nuts 102 described above to achieve and maintaincorrection of spinal deformity.

FIGS. 43-46 illustrate an apparatus 710 constructed in accordance with aseventh embodiment of the present invention. In the seventh embodimentof FIGS. 43-46, reference numbers that are the same as those used inFIGS. 1-11 designate parts that are the same as parts in FIGS. 1-11.

According to the seventh embodiment, the apparatus 710 includes ananchor 720 for implanting in a vertebrae 712 (FIG. 46). The anchor 720is made from a biocompatible material, such as titanium or stainlesssteel. It is contemplated that the biocompatible material used for theanchor 720 could also be polymeric or composite (i.e., carbon fiber orother biologic composite) in nature.

The anchor 720 is centered about a longitudinal axis 722 (FIG. 1). Theanchor 720 includes a platform 724 having a cylindrical outer surfaceportion 726 extending between oppositely disposed first and second axialends 728 and 730 of the platform. The platform 724 includes a generallyrectangular slot 732 that extends axially from the first end 728 towardthe second end 730 of the platform. Adjacent the first end 728, theouter surface 726 of the platform 724 includes first and second segmentsof external threads 734 and 736 that are separated by the slot 732. Theslot 732 and the threads 734 and 736 provide structure for connectingspinal fixation instrumentation to the platform 724 as discussed furtherbelow.

The platform 724 further includes a tunnel 740 and a plurality ofparallel passages 744 extending through the platform 724. As best seenin FIG. 44, the tunnel 740 extends transverse to and through the axis722. The tunnel 740 has an elliptical cross-section. Each of thepassages 744 extends transverse to the tunnel 740 and intersects thetunnel. In the illustrated embodiment, a centrally located first passage745 extends through the axis 722. Second and third passages 746 and 747are located on either side of the centrally located first passage 745.It should be understood that the platform 724 could have more or lessthan three passages 744.

The second end 730 of the platform 724 includes an end surface 738 (FIG.45) having a shape that is complimentary to the shape of a concave sidesurface 714 (FIG. 46) on the vertebrae 712. It should be understood thatthe end surface 738 of the platform 724 could be any shape necessary toremain complimentary to the shape of the side surface 714 of thevertebrae 712. The end surface 738 of the platform 724 may include barbs(not shown) or other suitable structure for fixedly engaging the sidesurface 714 of the vertebrae 712. Further the end surface 738 of theplatform 724 may also be porous, pitted, or have a biocompatible surfacecoating to assist with fixation of the anchor 720 to the vertebrae 712.

A fastener portion 750 of the anchor 720 projects from the second endsurface 738. The fastener portion 750 has a solid cross-section, butcould alternatively have a hollow or tubular cross-section. It iscontemplated that, with a tubular cross-section, the wall thickness canbe varied/selected to match the modulus of elasticity of the bone, whichcan improve fixation strength and load-sharing characteristics of theanchor 720 and the vertebrae 712.

The fastener portion 750 comprises a shaft 752 with an external threadconvolution 754 for engaging the vertebrae 712. The thread convolution754 is a known coarse helical pattern that extends about the axis 722.Although the outer surface of the fastener portion 750 is shown as beingsmooth, it is contemplated that the outer surfaces may instead beporous, pitted, or have a biocompatible coating to assist with fixationof the anchor 720 to the vertebrae 712.

The fastener portion 750 includes a pointed tip 758. It is furthercontemplated that the tip portion 758 could be covered with a tipprotector (not shown) to prevent accidental sticks to surgical staff andaccidental damage to tissue surrounding the vertebrae. Such a tipprotector could be made of a bio-absorbable material, such as polylacticacid, or non-bio-absorbable material, such as medical grade silicon. Thetip protector would be manually removed or pushed-off duringimplantation of the anchor 720.

The apparatus 710 includes a staple 760 made of a suitable biocompatiblematerial such as titanium or stainless steel. The staple 760 has agenerally rectangular shape with an opening 762 for receiving theplatform 724 of the anchor 720. A plurality of nail-like projections 770extend from a lower surface 772 of the staple 760. In the illustratedembodiment, the projections 770 are disposed adjacent the four cornersof the staple 760 and are for embedding into the vertebrae 712.

The apparatus 710 for correcting spinal deformity further includes therod 70, the bar 100, the lock nut 102, and the cables 120, 150 and 170described above with regard to the first embodiment. As previouslydescribed, one or more of the cables 120, 150 and 170 are used tostraighten curvature in the spine prior to attachment of the bar 100 tothe anchor 720.

To implant the anchor 720, a pilot hole (not shown) may be drilled inthe cortical bone of the vertebrae 712. The tip portion 758 of thefastener portion 750 of the anchor 720 is then placed in the hole in thevertebrae 712 and the rotatable driver 130 (FIG. 45) is inserted intothe slot 732 in the platform 724. The driver 130 is then rotated,causing the anchor 720 to rotate as well. Rotation of the anchor 720screws the fastener portion 750 into the cancellous bone of thevertebrae 712. Continued rotation of the anchor 720 embeds the fastenerportion 750 deeper into the cancellous bone of the vertebrae 712. Theanchor 720 is rotated until the end surface 738 of the platform 724seats against the side surface 714 of the vertebrae 712 as shown in FIG.46.

The staple 760 is then placed over the platform 724 of the anchor 720and force is applied to the staple to drive the projections 770 into thevertebrae 712. The projections 770 are driven into the vertebrae 712until the lower surface 772 of the staple 760 contacts the surface 714of the vertebrae. In this position, as shown in FIG. 46, the inwardlyfacing surfaces of the staple 760 engage the periphery of the platform724 to block relative movement between the anchor 720 and the staple.This prevents the anchor 720 from rotating and backing out of thevertebrae 712 and provides stability for the platform 724.

Once two or more of the anchors 720 and associated staples 760 have beenimplanted in separate vertebrae, one or more of the cables 120, 150 and170 described above can be used, along with the bar 100 and nuts 102, toachieve and maintain correction of spinal deformity.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. For example, itis contemplated that more than two cables could be used with theapparatuses disclosed above in order to achieve correction in multipleplanes. Such improvements, changes and modifications within the skill ofthe art are intended to be covered by the appended claims.

Having described the invention, I claim:
 1. An apparatus for correctingspinal deformity, said apparatus comprising: at least one anchor forimplantation into a vertebral body, said at least one anchor including aplatform having a first surface for facing the vertebral body; saidplatform including a tunnel and at least one passage extending throughsaid platform, said at least one passage extending transverse to saidtunnel and intersecting said tunnel; said at least one anchor includingscrew means for embedding into the vertebral body upon rotation of saidplatform, said screw means projecting from said first surface on saidplatform and extending along a longitudinal axis; and a removable rodextending into said tunnel in said platform, said removable rod havingat least one opening for receiving a cable connected with anothervertebral body.
 2. The apparatus of claim 1 wherein said platformincludes a plurality of parallel passages extending transversely throughsaid platform and transverse to said tunnel, each of said plurality ofparallel passages for receiving connecting means for connecting saidremovable rod to said platform.
 3. The apparatus of claim 2 wherein saidremovable rod includes a plurality of parallel openings, at least one ofsaid plurality of parallel openings being alignable with at least one ofsaid plurality of parallel passages in said platform and being adaptedto receive the connecting means.
 4. The apparatus of claim 3 furthercomprising at least one cable extending through one of said plurality ofparallel openings in said removable rod.
 5. The apparatus of claim 4wherein said at least one anchor comprises first and second anchors forimplanting in first and second vertebral bodies, respectively, said atleast one cable extending through a respective one of said plurality ofparallel openings in said removable rod associated with each of saidfirst and second anchors, said at least one cable being tensionable tocause relative movement between the first and second vertebral bodies.6. The apparatus of claim 5 wherein said platform on each of said firstand second anchors includes structure for connecting a spinal fixationimplant.
 7. The apparatus of claim 6 further comprising a spinalfixation implant extending between and connected to said platform oneach of said first and second anchors after said at least one cable hasbeen tensioned to effect relative movement between the first and secondvertebral bodies.
 8. The apparatus of claim 5 wherein said at least onecable includes a primary cable extending through a first one of saidplurality of parallel passages in said platform of each of said firstand second anchors and through a second one of said plurality ofparallel openings in said removable rod.
 9. The apparatus of claim 8wherein said at least one cable further includes a secondary cableextending between a second one of said plurality of parallel openings ineach of said removable rods associated with said first and secondanchors, said secondary cable being tensionable to cause relativemovement between the first and second vertebral bodies in one directionafter said primary cable has been tensioned to effect relative movementbetween the first and second vertebral bodies in another direction. 10.The apparatus of claim 1 wherein said screw means comprises anexternally threaded fastener.
 11. The apparatus of claim 1 wherein saidscrew means comprises at least one helical spike extending around saidlongitudinal axis.
 12. The apparatus of claim 11 wherein said screwmeans comprises two helical spikes spaced 180° apart around saidlongitudinal axis.
 13. The apparatus of claim 11 wherein said screwmeans comprises three helical spikes spaced 120° apart around saidlongitudinal axis.
 14. The apparatus of claim 11 wherein said at leastone helical spike, when implanted, has a conical shape that increases indiameter as said at least one helical spike extends away from saidplatform.
 15. The apparatus of claim 11 wherein at least a portion ofsaid at least one helical spike is made of a shape memory alloy that isresponsive to changes in temperature above and below a predeterminedtemperature transition range, said at least one helical spike being insaid first condition when the temperature of said at least one helicalspike is below said predetermined temperature transition range, said atleast one helical spike being in said second condition when heated abovesaid predetermined temperature transition range, said at least onehelical spike being implanted into the vertebral body in said secondcondition.
 16. The apparatus of claim 15 wherein said at least onehelical spike further has a connecting portion at a proximal endconnected to said platform and an intermediate portion extending betweensaid connecting portion and a tip portion, at least one of saidintermediate portion and said tip portion being made of said shapememory alloy.
 17. The apparatus of claim 11 wherein said at least onehelical spike has a solid cross-section.
 18. The apparatus of claim 11wherein said at least one helical spike has a tubular cross-section. 19.The apparatus of claim 11 wherein a first portion of said at least onehelical spike has a solid cross-section and a second portion of said atleast one helical spike has a tubular cross-section.
 20. An apparatusfor correcting spinal deformity, said apparatus comprising: first andsecond anchors for implantation into first and second vertebral bodies,respectively, each of said first and second anchors including a platformhaving a tunnel and at least one passage extending through saidplatform, said at least one passage in each of said anchors extendingtransverse to and intersecting said tunnel in each of said anchors; eachof said first and second anchors further including screw means forembedding into a respective one of the vertebral bodies upon rotation ofsaid platform, said screw means projecting from said platform on each ofsaid first and second anchors; a first removable rod extending into saidtunnel in said platform of said first anchor and a second removable rodextending into said tunnel in said platform of said second anchor, eachof said removable rods having at least one opening; and at least onecable extending through said at least one opening in each of saidremovable rods, said at least one cable being tensionable to causerelative movement between the first and second vertebral bodies.
 21. Theapparatus of claim 20 wherein said platform on each of said first andsecond anchors includes a plurality of parallel passages extendingtransversely through said platform and transverse to said tunnel in eachof said platforms, each of said plurality of parallel passages forreceiving connecting means for connecting said removable rods to saidplatforms.
 22. The apparatus of claim 21 wherein each of said removablerods includes a plurality of parallel openings that are alignable withsaid plurality of parallel passages in said platform and are adapted toreceive the connecting means.
 23. The apparatus of claim 22 wherein saidplatform on each of said first and second anchors includes structure forconnecting a spinal fixation implant.
 24. The apparatus of claim 23further comprising a spinal fixation implant extending between saidplatform on each of said first and second anchors, said spinal fixationimplant being fixedly connected to each of said first and second anchorsafter said at least one cable has been tensioned to effect relativemovement between the first and second vertebral bodies.
 25. Theapparatus of claim 24 wherein said at least one cable includes a primarycable extending through a first one of said plurality of parallelpassages in each of said platforms and through a first one of saidplurality of parallel openings in said removable rods disposed in saidtunnels in said platforms.
 26. The apparatus of claim 25 wherein said atleast one cable further includes a secondary cable extending between asecond one of said plurality of parallel openings in each of saidremovable rods associated with said first and second anchors,respectively, said secondary cable being tensionable to cause relativemovement between the first and second vertebral bodies in one directionafter said primary cable has been tensioned to effect relative movementbetween the first and second vertebral bodies in another direction. 27.The apparatus of claim 20 wherein said screw means on each of said firstand second anchors comprises an externally threaded fastener.
 28. Theapparatus of claim 20 wherein said screw means on each of said first andsecond anchors comprises at least two helical spikes.
 29. The apparatusof claim 28 wherein said at least two helical spikes on each of saidfirst and second anchors, when implanted, have a conical shape thatincreases in diameter as said at least two helical spikes extend awayfrom said platform on each of said first and second anchors.
 30. Anapparatus for correcting spinal deformity, said apparatus comprising: atleast two anchors for implantation into separate vertebral bodies,respectively, each of said at least two anchors including a platformhaving a tunnel and at least one passage extending through saidplatform, said at least one passage in each of said at least two anchorsextending transverse to and intersecting said tunnel in each of saidanchors; each of said at least two anchors further including screw meansfor embedding into a respective one of the vertebral bodies uponrotation of said platform, said screw means projecting from saidplatform on each of said at least two anchors; a first removable rodextending into said tunnel in said platform of one of said at least twoanchors and a second removable rod extending into said tunnel in saidplatform of another of said at least two anchors, each of said removablerods having at least one opening; at least one cable extending throughsaid at least one opening in each of said removable rods, said at leastone cable being tensionable to cause relative movement between thevertebral bodies; and a spinal fixation implant extending between andconnectable with said platform on each of said at least two anchors. 31.The apparatus of claim 30 wherein said platform on each of said at leasttwo anchors includes a plurality of parallel passages extendingtransversely through said platform and transverse to said tunnel in eachof said platforms, each of said plurality of parallel passages forreceiving connecting means for connecting said removable rods to saidplatforms.
 32. The apparatus of claim 31 wherein each of said removablerods includes a plurality of parallel openings that are alignable withsaid plurality of parallel passages in said platform and are adapted toreceive the connecting means.
 33. A method for correcting spinaldeformity, said method comprising the steps of: providing at least twoanchors for implantation into separate vertebral bodies, each of the atleast two anchors including a platform having a tunnel and at least onepassage extending through the platform, the at least one passageextending transverse to the tunnel and intersecting the tunnel, each ofthe at least two anchors further including screw means for embeddinginto one of the vertebral bodies upon rotation of the platform;providing at least two removable rods, each of which has a plurality oftransversely extending openings; implanting the at least two anchors inthe separate vertebral bodies; inserting one of the removable rods intothe tunnel in each of the at least two anchors; aligning one of theplurality of openings in each of the removable rods with the at leastone passage in each of the platforms; inserting connecting means intoeach of the aligned one of the plurality of openings and the at leastone passage to connect a respective one of the at least two removablerods with each of the at least two anchors; connecting the at least twoanchors with at least one cable that extends through another of theplurality of openings in each of the removable rods; and tensioning theat least one cable to cause relative movement between the vertebralbodies.
 34. The method of claim 33 further comprising the step of:connecting a spinal fixation implant to the platform on each of the atleast two anchors.
 35. The method of claim 33 wherein the platform oneach of the at least two anchors includes a plurality of parallelpassages extending through the platform and transverse to the tunnel ineach of the at least two anchors.
 36. The method of claim 35 whereinsaid step of connecting the anchors with at least one cable comprisesthe steps of: extending a primary cable between one of the plurality ofopenings in the removable rod connected to each of the at least twoanchors; and tensioning the primary cable to cause relative movementbetween the vertebral bodies in one direction.
 37. The method of claim36 wherein said step of connecting the anchors with at least one cablefurther comprises the steps of: extending a secondary cable betweenanother of the plurality of openings in each of the removable rods; andtensioning the secondary cable to cause relative movement between thevertebral bodies in another direction.
 38. The method of claim 37further comprising the step of: connecting a spinal fixation implant tothe platform on each of the at least two anchors.